Field of the Invention
The present invention relates to a video-on-demand service and more specifically to a system of effectively controlling the video-on-demand service.
With the increasing popularity of cable television (CATV), a lot of video-on-demand services have been provided for subscribers through CATV networks.
The video-on-demand (hereinafter referred to as VOD) service is an interactive system for transmitting video data, requested by a subscriber through a terminal device called a set top box (STB) mounted in each subscriber's home, from the CATV center that stores films pictures identified by plural titles.
The above described CATV center is connected to a plurality of CATV subscribers' homes to distribute video data to the subscribers along a plurality of video channels over the CATV network. The CATV center reads using the built-in video server the video data requested by the subscriber from the video storage device, digitally modulates the video data, and distributes the data to the subscribers' homes through the CATV network. The video data distributed to the subscribers are demodulated by the STB at the subscribers' homes and displayed on the screens of the TV receivers.
The VOD service can be either an NVOD (near video on demand) service or an FVOD (full video on demand) service. The NVOD service has been realized in the U.S. while the FVOD service is being developed in many other countries.
The FVOD service is a service through which the subscribers can immediately request and watch a desired program recorded on video. At the request of a subscriber, the requested video is played immediately. The subscriber can also exclusively watch a specified program recorded on video. Therefore, the FVOD service, as with the home video tape recorder and video disk, enables the subscriber to not only play but also fast-forward, rewind, and pause the video. To realize these capabilities, the FVOD service requires use of an exclusive channel for each subscriber.
On the other hand, the NVOD service is also referred to as a time shift service, that is, it broadcasts a program recorded on a video along plural channels at predetermined time intervals. Practically, 6 channels are used to start broadcasting a 2-hour program at 20-minute intervals. The subscribers can watch the program from the beginning by waiting for 20 minutes at most.
The FVOD and NVOD services are described below by referring to the flowcharts shown in FIGS. 1 and 2.
FIG. 1 is a flowchart showing the outline of the services through the FVOD service.
The subscriber selects a desired title from a plurality of titles provided by the FVOD service and displayed on the screen of a television receiver using his or her own STB. The STB transmits the signal indicating a request to watch the program identified by the selected title (S1) to the CATV center through the CATV network.
When the CATV center receives the request signal through the CATV network, it recognizes the title requested by the subscriber (S2).
Using the internal busy-management mechanism, the CATV center calculates the current busy level of the video server for performing a stream process on the video data of the program identified by the requested title (S3).
The busy level can be represented by, for example, the number of current accessing operations to a video server. The video server places a limitation on the number of subscribers who can be simultaneously provided with the FVOD service depending on the video data transmission capabilities of the CPU, data transfer capabilities of the video storage device that stores the video data, and the data transfer speed of the bus connecting the CPU with the video storage device. Therefore, a threshold for the number of subscribers simultaneously watching a program is preliminarily set in the video server. When a new request is received and the busy level exceeds the threshold for the number of the audiences simultaneously enjoying the program, the video server is in a busy state in which video data cannot be distributed to the new subscriber.
If it is determined by the busy management mechanism that the video server is not in the busy state, the CATV center assigns to the subscriber a video channel for distributing the video data requested by the subscriber, and transmits the video channel information to the STB of the subscriber through the CATV network (S4).
Upon receipt of the above described video channel information, the STB sets his or her receiving channel to the channel number specified in the information.
Then, the CATV center reads from the video storage device the video data having the title specified by the subscriber. After being digitally-modulated, the video data is transmitted to the STB through the CATV network (S5).
Thus, the subscriber can watch the video data through the FVOD service.
If it is determined in step S3 that the CATV center is busy, it transmits to the subscriber's STB through the CATV a message that the request cannot be accepted (S6).
Therefore, the subscriber cannot watch the desired video data.
FIG. 2 is a flowchart showing the outline of the NVOD service.
The subscriber selects a desired title from a plurality of titles provided in the NVOD service and displayed on the screen of the television receiver using his or her STB. The STB transmits to the CATV center through the CATV network the signal indicating the request to watch the video data having the selected title (S11).
When the CATV center receives the request signal through the CATV network, it recognizes the title requested by the subscriber (S12).
The CATV center assigns to the subscriber a video channel for distributing the video data requested by the subscriber, and transmits the video channel information to the STB of the subscriber through the CATV network. The STB sets his or her receiving channel to the channel number specified by the information (S13).
When it is time to broadcast the requested program, the CATV center reads the subscriber-requested video data from the video server, digitally modulates the data, and distributes through the CATV network the data along the channel assigned to the subscriber (S14).
Thus, the subscriber can request and watch the program recorded on video at a predetermined time.
The FVOD service is described below more practically by referring to FIGS. 3 and 4.
The initial menu of the VOD service is displayed on the screen of the television receiver through the STB at the subscriber's home as shown by (1) in FIG. 3. The subscriber selects the FVOD service on the screen through the STB ((2) shown in FIG. 3).
Then, the category selection screen indicated by (3) shown in FIG. 3 is displayed. When the subscriber selects the latest program on the screen through the STB ((4) in FIG. 3), the title selection screen is displayed as indicated by (5) in FIG. 3.
If the subscriber selects the film "Speed" on the screen through the STB ((6) in FIG. 3), then this program is displayed on the latest preview screen as shown by (7) in FIG. 3. If "Speed" has already been provided to a number of other subscribers, the CATV center may reject the request.
Then, the subscriber pushes the OK button on the preview screen through the STB ((8) in FIG. 4). Thus, "Speed" is distributed by the CATV center to the subscriber's STB, and "Speed" is played back on the screen of the subscriber's receiver ((9) in FIG. 4).
Next, the operations of the NVOD service are described more practically by referring to FIGS. 5 and 6.
The initial menu of the VOD service is displayed on the screen of the television receiver through the STB at the subscriber's home as shown by (1) in FIG. 5. The subscriber selects the NVOD service on the screen through the STB ((2) shown in FIG. 5).
Then, the category selection screen indicated by (3) shown in FIG. 5 is displayed. When the subscriber selects the latest program on the screen through the STB ((4) in FIG. 5), the latest program broadcast schedule screen is displayed as indicated by (5) in FIG. 5. On this screen, the video broadcast schedule is displayed in, for example, alphabetical order of the broadcast programs. The broadcast schedule is predetermined by the manager of the CATV center.
If the subscriber selects "Speed" on the screen through the STB ((6) in FIG. 5), then "Speed" is displayed on the preview screen as shown by (7) in FIG. 5. Additionally, the message, "Speed" will be broadcast after .oval-hollow..oval-hollow. minutes. Do you want to watch it?" is displayed on the preview screen. Furthermore, the CANCEL and OK buttons are displayed at the lower part of the preview screen.
If the subscriber pushes the OK button on the preview screen through the STB ((8) in FIG. 5), the service screen, etc. is displayed until "Speed" starts.
Thus, "Speed" is distributed after .oval-hollow..oval-hollow. minutes by the CATV distributing device to the subscriber's STB, and "Speed" is played back on the screen of the subscriber's receiver ((9) in FIG. 6).
Described below are some of the problems in the above described conventional VOD services.
FIG. 7 is a block diagram showing the outline of the problems.
When the subscriber requests and selects the video data, he or she should also select either the FVOD or NVOD service, thereby giving the subscriber a problem.
If the subscribers' requests concentrate on a specific program in the FVOD service, and if the concentration exceeds the limit of the video transmission capacity of the video server and the busy management mechanism determines too many requests, then the requests from some subscribers will be rejected, thereby failing to fully satisfy the subscribers.
In the NVOD service, the program is broadcast at predetermined time intervals regardless of whether any subscribers are watching the program. Therefore, if there is only a small number of subscribers, there is the possibility that no subscribers are watching the requested program at the start of a certain broadcast time. Some programs may be watched by no subscribers. This is a waste of the resources of the CATV center and therefore losses are incurred. The operation manager of the CATV service is required to organize the video programs and fix time schedules for the programs, which creates problems for the manager.